This invention relates to conductive coatings and specifically to a nonstick conductive coating for use with an electrosurgical cutting instrument.
Electrosurgical devices or surgical cutting blades, which are adapted to use radio frequency electrical energy in the performance of hemostatic surgery, are disclosed in commonly owned copending related United States patent applications of Herczog, U.S. Ser. No. 961,192, and Herczog et al., U.S. Ser. No. 961,189. Other such hemostatic surgical instruments are available in the prior art, for example, see U.S. Pat. No. Re. 29088 for a heated surgical scalpel. There are other variations on the concept of hemostatic surgery including systems utilizing electric discharge to cut and cauterize, and related systems such as shown in U.S. Pat. Nos. 4,161,950, 4,033,351 and 3,913,583.
While the concept involved in the present invention might be adapted for use in many of the aforementioned electrosurgical devices, it is best exemplified for its usefulness in the cutting instruments of the type disclosed in Herczog et al. (hereinafter the Herczog or RF blade). In a preferred system, electrical source generated hemostatic and cauterizing currents are carried to separate electrodes which are deposited near the edge of the blade. Moisture from incised tissue surfaces completes a circuit from one electrode to the other and the high frequency source generated currents pass through the tissue, generate heat and cause hemostasis in the vicinity of the electrodes.
In such a system it is possible for the blade to stick to the tissue in the incision, thereby causing apparent dullness of the blade. The problem is alleviated when non-stick coatings are used, however, because of the nature of non-stick materials, many tend to be fragile and are abraded easily. Thus, the non-stick properties tend to degrade in normal use, due in part to actual cutting, and partly due to the frequent wiping necessary in order to remove surgical debris adhered to the blade. When sticking is severe, the blade is unfit for further use and must be discarded. Further, when using the Herczog concept, the non-conductive nature of most non-stick films tends to interfere with the conductivity of the electrodes.
There are a number of patents in the prior art disclosing non-stick coatings. These patents mainly relate to the use of fluorocarbon polymers on razor blades for increasing their lubricity and enhancing the comfort of such shaving instruments while in use. Such arrangements are described in U.S. Pat. Nos. 4,012,551 and 3,754,329. There are also electrosurgical instruments having non-stick coatings, but none approach or contemplate the problems unique to RF blades.
Organic fluorocarbon materials such as those sold by E. I. DuPont de Neumoirs under the registered trademark TEFLON.RTM. may be used in conventional instruments. However, since such materials are nonconducting it is difficult to achieve the conductivity required for RF applications. If the electrodes are insulated, they become ineffective for the purpose of hemostatic surgery in accordance with the Herczog blade concept.
The present invention solves many of the aforementioned problems by providing a conductive coating manufactured as the composite of a first layer of conductive material adherently deposited on the instrument and a second coating of non-stick material deposited on and within the first coating. The second coating at least partially fills microscopic irregularities or interstices in the first, such that the non-stick coating is able to adhere thereto. The nonstick coating is then partially removed while still moist such as by wiping, so that high profile points in the conductive coating are exposed, thus allowing the electrodes to be sufficiently conducting while exhibiting a satisfactory non-stick characteristic. The conductive layer is provided with sufficient roughness so that the non-stick coating will more firmly adhere thereto and resist erosion or peeling.